1. Field of the Invention
This invention relates to a torch ignition type internal combustion engine, and more particularly to a torch ignition type internal combustion engine which has no intake valve in the auxiliary combustion chamber.
2. Description of Prior Art
It is well known in the art to burn a rather lean air-fuel mixture in the engine cylinder in order to reduce the toxic components such as carbon monoxide, hydrocarbons and nitrogen oxides which are usually present in the engine exhaust. A lean air-fuel mixture, however, has inferior ignition properties and inferior flame propagation velocity, allowing raw air-fuel mixture to blow by to the exhaust manifold and causing reductions in the cyclic thermal efficiency.
In order to overcome the aforementioned difficulty, there has been introduced the so-called torch ignition type internal combustion engine which has a main combustion chamber with an intake valve and an exhaust valve, and an auxiliary combustion chamber with an intake valve, the engine being adapted to supply a lean air-fuel mixture to the main combustion chamber and a relatively rich mixture to the auxiliary combustion chamber through the respective intake valves. In such an engine system, the relatively rich air-fuel mixture in the auxiliary combustion chamber is first ignited and burned, the flames bursting from the auxiliary combustion chamber subsequently igniting the lean air-fuel mixture in the main combustion chamber. This internal combustion engine with an intake valve in the auxiliary combustion chamber has its own merits in that it ensures combustion of the lean air-fuel mixture and high flame propagation velocity. On the other hand, such internal combustion engine invariably has complicated construction due to the requirement for the provision of the intake valve in the auxiliary combustion chamber. Such a valve requires a complicated valve operating mechanism for opening and closing the same at a predetermined timing.
A torch ignition type internal combustion engine has previously been proposed which comprises a main combustion chamber with an intake valve and an exhaust valve, an auxiliary combustion chamber with no intake valve, a passage interconnecting the main and auxiliary combustion chambers, and an ignition plug having its sparking electrodes located in the auxiliary combustion chamber and in the vicinity of the interconnecting passage. In this torch ignition type internal combustion engine, a lean air-fuel mixture inhaled into the main combustion chamber through the intake valve during the intake stroke of the piston is urged into the auxiliary combustion chamber during the succeeding compression stroke through the passage interconnecting the main and auxiliary combustion chambers. Now that there is only fresh air-fuel mixture surrounding the sparking elctrodes of the ignition plug which is located in the auxiliary combustion chamber in a position near the passage, the lean air-fuel mixture within the auxiliary combustion chamber is ignited and burned without material interference from the exhaust which might be still remaining in the auxiliary chamber, followed by ignition of the lean air-fuel mixture in the main combustion chamber by the flames bursting out from the auxiliary combustion chamber.
With the above-described torch ignition type internal combustion engine with no intake valve in the auxiliary combustion chamber, it is necessary to reliably ignite and burn the lean air-fuel mixture passed into the auxiliary combustion chamber through the interconnecting passage. To this end, it is necessary to control the velocity and amount of the lean air-fuel mixture passed into the auxiliary combustion chamber through the interconnecting passage.